a) Field of the Invention
The invention relates to air-activatable polymerisable compositions and their use. The compositions are suitable for use as one-component systems for forming polymers, requiring no primers. The compositions are useful as adhesives, sealants, surface coatings, moulding resins and composite matrices, for example. These compositions are particularly suitable for use as thread-locking compounds, e.g. for cementing nuts to threaded shafts, bushes to bush housings and the like.
b) Description of the Related Art
The cure of acrylic adhesives is initiated by a two-part redox system. The first part, the initiator, is normally present in the base component of the adhesive and the second part is present in the accelerator or curative component. One widely used curative is the reaction product of aniline and n-butyraldehyde. The reaction product was first known from U.S. Pat. No. 1,780,334 assigned to E.I. Du Pont DeNemours and Co. The condensation of aniline and n-butyraldehyde results in many products, some having complex structures. However it appears that the major component and active ingredient is a substituted dihydropyridine (DHP).
An adhesive composition which can be formulated either as a two-part system or as a system utilising a primer is disclosed in U.S. Pat. No. 3,890,407, assigned to E.I. Du Pont DeNemours and Co. The composition comprises a sulphur-bearing component selected from chlorosulphonated polyethylene and a mixture of sulphonyl chloride with chlorinated polyethylene in at least one polymerisable vinyl monomer and an accelerator comprising a primary amine-aldehyde condensation product. U.S. Pat. No. 4,112,013 also of E.I. Du Pont DeNemours and Co. which was divided from U.S. Pat. No. 3,890,407 specifies that the chlorosulphonated polyethylene is made from branched polyethylene having a melt index of about 100, the chlorosulphonated polyethylene containing about 43% chlorine by weight and about 34 mmoles of sulphonyl chloride per 100 grams of polymer and the composition may also comprise a mixture of methyl-methacrylate, glacial methacrylic acid and ethyleneglycol dimethacrylate. A further U.S. Pat. No. 4,106,971, also divided from U.S. Pat. No. 3,890,407, relates to a method of bonding two surfaces comprising the above disclosed adhesive compositions.
A bonding accelerator containing a condensation reaction product of an aldehyde and a primary or secondary amine is known from U.S. Pat. No. 3,599,438, assigned to Loctite Corporation, together with a reducing activator comprising either a sulphur-containing free radical accelerator or a compound containing an oxidizable transition metal. Such a condensation reaction product is also known for use in conjunction with a polymerisable acrylate ester monomer and a peroxy polymerisation initiator (U.S. Pat. No. 3,616,040 also of Loctite Corporation).
U.S. Pat. No. 4,430,480, assigned to Loctite Corporation relates to an adhesive composition which comprises a first part comprising a solution of chlorosulphonated polyethylene in at least one polymerisable vinyl monomer, a polymerisation catalyst which comprises at least one free-radical initiator and a second part comprising an activator composition which consists of at least 70% of the condensation reaction product formed between butyraldehyde and aniline.
An improved adhesive composition of this type, enriched in N-phenyl-3,5-diethyl-2-propyl-1,2-dihydropyridine to a concentration of at least about 70% by weight of the condensation reaction products is known from U.S. Pat. No. 4,430,480.
All of the above compositions based on aldehyde-amine condensation reaction products are, however, two-part systems.
British Patent Specification No. 1113722 of Minnesota Mining and Manufacturing Company discloses aerobic compositions which are polymerisable in the presence of a free radical catalyst which comprises one or more mono- and/or bis-acrylate and/or methacrylate monomers which are blended with from 0.05 to 6% by weight of the monomer of a triaryl borane complex. British Patent Specification No. 1251737 of Toyo Soda Manufacturing Company Limited discloses the polymerisation of a vinyl monomer, chloroprene or methyl methacrylate in the presence of a catalyst comprising a trialkyl boron compound and a chloro hydrocarbon mixed in a molar ratio of 1:0.2 to 1:8.0.
The polymerisation of vinyl monomers using catalysts which are either diborane adducts or oligomers based on monomer units which contain at least two borane atoms are disclosed in U.S. Pat. No. 4,167,616 assigned to Rohm and Haas Company. The compositions also include an oxygen source.
U.S. Pat. No. 4,515,724 assigned to Henkel Kommanditgesellschaft Auf Aktien relates to boron alkyl compounds as initiators of free-radical polymerisation, the compounds being esters of a fatty acid or fatty alcohol having at least one boryl radical or organoboron radical attached thereto.
European Patent Application No. 0078994 A1 of Henkel KgaA describes an air-activatable starter system for the polymerisation of olefinic compounds, based on organo-boron compounds with improved storage stability even on admission of air, which consists of a homogeneous mixture of at least one organo-boron compound activatable by admission of air with at least one organic oligomer or polymer which at room temperature is fluid to solid and which is inert towards the organo-boron compound.
The majority of these borane compositions have been found to be "two part" systems with limited pot lives. Where one-component adhesives are described, difficulties are encountered in formulation and obtaining adequate stability.
An adhesive composition which is described as being polymerisable either aerobically or anaerobically is disclosed in U.S. Pat. Nos. 4,348,503, and 4,429,088 divided therefrom, of Bachmann, and comprises an acrylic ester monomer capable of free-radical polymerisation and a monomeric polyacrylate ester prepolymer together with a catalyst system which comprises an aromatic perester free-radical precursor, an organic acid and a soluble compound of a transition metal cure accelerator. However this composition requires a separate activator such as an amine-aldehyde condensate.
U.S. Pat. No. 4,452,955, assigned to Minnesota Mining and Manufacturing Company, discloses an adhesive composition comprising a polymerisable monomer having at least one alpha, beta-unsaturated carboxyl functionality and as an accelerator an organic sulphimide or perfluroalkylsulphonanilide, together with an inhibitor of free-radical polymerisation to retard polymerisation of the unsaturated carboxyl functionality on contact with the accelerator, and a condensation reaction product of an aldehyde and a primary or secondary amine.
Free radical polymerizable compositions are disclosed in European Patent Specification No. 0,356,875 of Henkel KGA. These comprise ethylenically unsaturated, polymerizable compounds together with an activator system which can be initiated by oxygen and water, comprising an N-alkyl-substituted tert-arylamine with at least one aliphatic CH bond in the alpha position, a metal compound generally used for accelerating the drying of unsaturated oil and which is at least partially soluble in the composition, and a compound of a weakly acidic carboxylic acid having a pKa value of no less than about 0.9, which can be hydrolyzed to a free carboxylic acid on contact with moisture.
The N-alkyl-substituted tert-arylamines correspond in particular to the general formula: ##STR2## in which R.sub.1 is an optionally substituted aryl radical, more especially an optionally alkyl-substituted phenyl radical, R.sub.2, has the same meaning as R.sub.1, or is an optionally substituted, linear or branched alkyl radical and R.sub.3, is a linear or branched alkyl radical which may be substituted, but contains at least one hydrogen atom in the alpha-position to the nitrogen.
These compositions depend on the action of both water and oxygen to effect a cure reaction. As such their formulations are very dependant on humidity conditions.
WO91/10687-A of Henkel KGaA published after the priority date of this Application describes radical-cured multicomponent mixtures stable in the absence of air which contain alkyl, cycloalkyl and/or aryl hydrazones of aldehydes and/or ketones as initiators which form hydroperoxides.